What the Mulder’s Chart Teaches Us About Fertility Plans

Providing crops with appropriate fertility can be a challenge for growers, especially when considering the importance of maintaining ROI. Plants, soil and the grower’s own fertility plan all play a role in crop health and yield. The Mulder’s Chart is a tool growers can use to better understand the ways nutrients interact with each other to benefit or even hinder the balance between soil and crop.

Written by Rachel Sim, with expertise provided by Nate Couillard, Senior Agronomist, Sound Agriculture.

Nutrient availability is impacted by a variety of factors, including soil pH and what form of the nutrient is applied. What is less well known, however, is that both macro- and micronutrients in the soil interact with each other to impact plant availability. Mulder’s Chart illustrates these relationships between nutrients and shows their tendency to antagonize each other in large amounts. 

“The Mulder’s Chart is our best attempt at diagramming what is occurring in the soil. It shows the interactions and complexity of nutrients, how they hurt or help other nutrients getting into the plants,” says Nate Couillard, Senior Agronomist at Sound Agriculture. 

It is not a prescriptive chart — it does not suggest amounts of nutrients or any specific course of action. Instead, it simply demonstrates the level of complexity growers are dealing with in their soil.

“The chart conveys that we’re trying to get our nutrients in balance, to harmonize in order to support soil operating in an optimized system,” says Nate.

Balanced and healthy soils support increased yield and improved plant health; when everything is functioning as intended, growers can achieve peak output. But just as growers can support a well-functioning system, there are things that can also throw the system off balance.

“There are things that we as growers can do that negatively impact the system too,” says Nate. ​“Just like a vehicle engine, when you tune it, you can cause additional problems.”

Unlike the Mulder Chart, Liebig’s Law of Minimums is very straightforward; it illustrates that yield cannot be increased with only a single input. Instead, yield is determined by whichever nutrient is most limiting. The prescription of Liebig’s Law is to make sure that plenty of any limiting nutrients are added to the field to avoid yield loss. While Mulder’s Chart doesn’t contradict Liebig’s Law, it does add complexity. 

“With Mulder’s Chart, we can see that there are still scenarios where you may lack one nutrient, but too much can also be harmful,” says Nate. ​“It encourages us to balance our nutrition.” 

There is no one-size-fits-all for balanced nutrition. For each grower and each field, it will look a little different based on factors like soil type, climate and management strategies. Nate encourages growers to rely on their in-season soil and tissue tests to determine their own field’s needs. 

“In some of the tissue tests we took this year, we saw nitrogen levels that actually fell into the excessive category,” says Nate. ​“We rarely think about what that means, because many growers have a ​“Law of Minimums” mindset; I’ll see what nutrients I have successfully gotten into my plant and make sure they’re in the medium or high range.” 

However, in excessive amounts, nitrogen can negatively impact the uptake of boron, potassium and copper, all of which are essential nutrients themselves and can cause plant growth and health to be limited. When nitrogen levels get high enough, growers will likely see diminishing returns.

“Many farmers are used to getting as much nutrient in the soil as possible,” says Nate. ​“Often, that’s what success looks like — but really, there is a negative change.”

One way growers can work to develop a more balanced nutrient profile in their soil and crops is with SOURCEⓇ, Sound’s microbiome activator. SOURCE is a molecule that mimics the plant-to-microbe signal to attract microbes already present in the soil and increase crops’ access to key soil nutrients.

Those tissue tests Nate looked at this year were part of a SOURCE trial. He says when they compared the high-nitrogen control samples to SOURCE-treated plants, the plants treated with SOURCE had nitrogen levels in the optimal range along with increases in micronutrients that can be negatively affected by excess nitrogen. 

“The trend we’re seeing is that SOURCE creates a more harmonious balance between these nutrients,” says Nate.

Another grower running a SOURCE trial called Nate last season to look at his corn. He said the area where he’d applied SOURCE had obviously taller, greener plants. 

“With a drone, you could see the difference clear as day,” says Nate. 

To find out what the visual differences meant, they took tissue samples from both the control and the SOURCE-treated plants. The tests showed that the SOURCE-treated plants had 3.5 times more iron in their tissue, which made sense since iron plays an important role in chlorophyll synthesis. 

“When we did soil tests, it was clear that phosphorus levels were causing iron tie up in the control strip. With SOURCE, we were able to get more iron into the plant,” says Nate. 

In the soil, phosphorus binds to minerals like iron, calcium and aluminum. Many growers are familiar with this phenomenon because it limits the available phosphorus in their soil, and Mulder’s Chart illustrates these minerals’ antagonism with phosphorus. SOURCE helps break those bonds, and freeing phosphorus also frees those minerals, making them more accessible to the crop. 

“SOURCE helps growers manage these intricacies, doing the heavy lifting for growers when it comes to balancing out their nutrient levels,” says Nate. ​“You could feed your plants more iron, but SOURCE is a better financial option because it’s freeing more than just one nutrient; it’s fostering relationships between nutrients.” 

Because Mulder’s Chart highlights the intricate ways key plant nutrients interact rather than offering prescriptive suggestions, trying to balance each one individually simply isn’t feasible. Nate points out that time is a valuable and limited resource for growers. 

“How much time do you really have to invest in perfectly balancing your soil?” he says. ​“A product like SOURCE can be thrown in the tank to go across the field with something else, and it will figure out some of those nutrient balances for you.” 

A grower’s success is often measured by the yield achieved each harvest, and in pursuit of increased yield gains, applying more fertilizer and nutrients can seem like the best option, especially when it comes to nitrogen. But growers are increasingly aware of the downsides of approaching fertility with this attitude; any nutrients not taken up by the plant represent a real financial loss. 

“More is not always better; it’s not going to take yields to the next level or push the bounds of soil and plant capabilities,” says Nate. 

The amount the plant is able to use can’t be expanded simply by increasing the availability of any one nutrient and, as Mulder’s Chart shows, it could actually be limiting a crop’s access to other important nutrients. The chart offers a way to think about fertility beyond just how much a plant can take up; it can expand a grower’s awareness about balanced nutrition in the soil and in plants. Nate says it also increases awareness of the potential negative impacts growers may be having on their soil. 

“In a business like this, you have lots of inputs and assets needed to run the operation,” he says. ​“But the most important asset is the soil you’re farming; without the soil, your operation is dead.”